This low cost combination of a
modem & cell phone is ideal for those
" remote remote" sites where
a phone line is impossible.

With the cost cellular service declining a
cell modem makes sense for Utility and Industrial applications.

AMPS
Advanced
Mobile
Phone
Service

The first cellular networks
where analog systems. The Advanced Mobile Phone Service (AMPS) is in wide use
even today, almost 25 years after it was introduced. AMPS was conceived by Bell
Labs in the 1970s,. The AMPS air interface is specified in
EIA/TIA-553. AMPS is
based on FDMA.

The FCC allocated a total of
50 MHz (25 MHz on the A side and B side) in the 800-MHz spectrum for AMPS. Each
voice channel is allocated a 30-KHz portion of the bandwidth within the AMPS
frequency allocations. Which limits the number of channels for voice traffic to
312 calls at one time? AMPS uses the seven-cell frequency reuse method. Control
channels are used to set up and clear calls as well as other control messages.
Each band (25 MHz) contains 21 control channels. When a mobile station is not in
session, it must monitor designated control channels. It tunes and locks into
the strongest channel to receive system information. The forward control channel
(FOCC) is a data stream from the base station to the mobile, and the reverse
control channel (RECC)
is from the mobile to
the base station. Voice conversation is carried over the forward voice channel (FVC)
and the reverse voice channel (RVC)..

The ESN (Electronic
Serial
Number)
for a mobile is a 32-bit number that uniquely identifies a mo­bile and is set up
by the mobile manufacturer.

The system IDs SID (System
IDentification)
is a 15-bit binary numbers that are assigned to cellular systems. One of the
uses of the SID is to determine a home network from a roaming network.

The
MIN
(Mobile
Identification
Number)
is a 34-bit number that is derived from the mobile terminal's 10-digit telephone
number.

Data
services in AMPS
are straightforward and analogous to dial-up net-working. Because AMPS is an
analog technology, it is possible to make use of standard modems directly with
AMPS. Data rates are at a maximum of 14.4 Kbps irrespective of the modem
protocol (v.90 or others).

CDMA Online (contains an enormous
amount of information about how CDMA works)

What is CDPD

CDPD (Cellular Digital
Packet Data) is a specification for supporting wireless access to the Internet
and other public packet-switched networks. Cellular telephone and modem
providers that offer CDPD support make it possible for mobile users to get
access to the Internet at up to 19.2 Kbps . Because CDPD is an open
specification that adheres to the layered structure of the Open Systems
Interconnection (OSI) model, it has the ability to be extended in the future.
CDPD supports both the Internet's IP protocol and the ISO Connectionless Network
Protocol (CLNP).

CDPD also supports IP
multicast (one-to-many) service. With multicast, a company can periodically
broadcast company updates to sales and service people on the road or a news
subscription service can transmit its issues as they are published. It will also
support the next level of IP, IPv6.

For the mobile user, CDPD's
support for packet-switching means that a persistent link isn't needed. The same
broadcast channel can be shared among a number of users at the same time. The
user's modem recognizes the packets intended for its user. As data such as
e-mail arrives, it is forwarded immediately to the user without a circuit
connection having to be established. There is a circuit-switched version, called
CS CDPD, that can be used where traffic is expected to be heavy enough to
warrant a dedicated connection.

as you may well know the FCC
has let the carriers discontinue the CDPD networks
which are now being replaced by the GPRS and 1xRTT digital networks that run on
the IP networks